[CNGBiFuel]

Here’s an FAQ for factory Bifuel Volvos and after-market conversions running LPG / CNG.

Volvo were just about the first major manufacturer to bring both LPG and CNG cars to market.
The first few pointers will equally apply to those of you with aftermarket converted cars. The remainder are biased towards the rarer factory-fit 1997-2006 Bifuel cars. All the early 1997-2000 P80 cars and the later P2 V70s S80, S60s were fitted the same Necam/Koltec system.

These cars got an unjustly bad reputation. Volvo’s own support to their dealers was poor, and because the cars were not understood, dealers soon became frightened of them. Historically for similar reasons, and parts prices, the LPG / CNG conversion industry also avoided them. This left owners with limited options.

First the general points…
LPG or CNG gases are harder to ignite. Hence, whereas running petrol will be fine, running either LPG or CNG finds the weaknesses of any slightly tired, high-miler ignition system. Look to you plugs and coils first.

1) Steer clear of multi-point plugs. Spark plugs in these cars don’t want to be anything special. Good quality low-spec single-point are fine. Avoid Snake-oil LPG plugs, (NGK & Brisk brand etc). If you have the 5-pot B5244SG engine as fitted to the S80 & V70 factory Bifuels, you need Denso’s or NGK’s most basic plugs:

Denso K20PR-U
NGK BKR6ES

The S40
NGK BKR6es

Delivered to your door, a set of 5 will cost you no more than £10-12. There are no gains with ’so-called’ LPG plugs at 3-4 times the price. Brisk plugs might actually be worse.

IMPORTANT: Running petrol, there is an ongoing dispute about which is the correct plug-gap. Plugs are usually pre-gapped at 0.9mm. Running gas, reduce the gap to 0.7mm or 0.028 thou. Swapped every 15-20,000, I’ve found Denso K20PR-U at 0.7mm gap are best. Some will tell you wider gaps are fine, but often LPG or CNG will cause mis-firing to one or two cylinders. This is all the more prevalent if anything is tired, These cars are getting old. This brings me to…

2) Coil packs: These are a known issue. Combined with a wide plug-gap a car that runs OK on petrol runs lumpy on tired coil-packs with gas. Faulty coil-packs are easy to locate. With the car running, pull the connector from each respective coil-pack. The one that least effects smooth-running is your kiddy. Replace the plugs whilst you’re on…

The Necam System - Overview:
With an unjust reputation the factory-fit Necam system falls foul to many a bar-room mechanic. Mention Necam and you’ll struggle to hear anyone unable to resist telling you to be ripping everything out, and start again.
The issues the Necam system does have are usually sorted for under £200 - £400. A ‘better’ system, even if you install yourself, runs to £6-700 and the hassle. For most of us, the whole point of running LPG or CNG was to save money, and to put something else in there, a pro will want nearer £1700-2000.

The Necam system has a few known issues, and once you understand these, if all you want is for your car to run, it works well enough.

The Necam System
The Achilles-heel of the system is the hard working distributor / stepper motor assembly. Most issues come down to dirt and lack of maintenance and/or heat. Maintenance is made ever more awkward by the daft place Volvo have sited the distributor / stepper motor assembly on the post 2000 P2 Volvos. Pre 2000 P80 P1 cars suffer far less problems simply because the distributor / stepper motor assembly is mounted out of the heat on the bulkhead. More on this later.

Maintenance: Cleaning the distributor. (aka dizzy).
Because getting to it is such a faff, a short-cut on late cars is to pour injector cleaner down via the 16mm dizzy feed pipe. This sometimes works. LPG in particular is dirty stuff. The ‘heavy-ends’ clog the ‘V’ shaped slots found in the distributor giving poor starting and lumpy running. These ‘heavy-ends’ jam the piston of the expensive stepper motor. Hence often you’ll burn it out this way. It’s a hard-working part of your car. On the later cars getting to the stepper is a PITA. If you stepper motor was cheap, and a £40 item I wouldn’t worry. But it’s a £350-400 item, and that’s if you can find onet, he price and rarity of stepper motors makes this job not one to be skipped. Be aware, Volvo dealers want £65 for new stepper.

Cleaning is a 2-3 min job on early cars. On post 2000 cars look to 1-2 hours and grazed knuckles…

For 2001-2005 era S80 S60 V70s:
The stepper motor is even hard to find. It sits between the radiator and the engine block.

With the car running on gas disconnect the solenoid cable under the air box to purge the system of gas. Reconnect before you forget.

Disconnect battery. The distributor is close to some chunky cables that can supply lots of amps if you put a spanner in the wrong place!

Clamp the lower power-steering hose near the pump and disconnect the top hose and move out of the way. (Don't get oil in the alternator) Unbolt the dip stick pipe (10mm socket]. You don't have to remove it but it's easier if you do. Remove the pipes and cables and undo the 2 nuts on the distributor / engine bracket / rubber mount. Careful here, the rubber might be perished. If you do shear the rubber mount, Demon Tweeks Part No. FSEFPA905 - Facet Fuel Pump Mount x 2 will fit). Leaving the bracket on the distributor might be easiest. Remove; some jiggling required. Knuckles will be in fine order about now. Now replace those bracket nuts with wing-nuts. You'll be taking it off again in the future, so make it easy. And do not smoke!
Undo the hose and the two electrical plugs.

For pre 2000 era cars.
Sitting on the bulkhead, you can usually get away with leaving the distributor in place.

Removing the stepper motor from the distributor.
Remove 2 x 3mm Allen bolts and remove stepper motor. Careful here. Two reasons, 1) Shaft of stepper easily bent. 2) A* large spring washer about the size of a 2p bit, a large compression-spring, and if you’re unlucky a ball-bearing will fly around too. Watch yourself.

Unclip piston from the spring on the motor’s piston/plunger-tip* (note which way up piston goes - deeper side away from stepper to accommodate large compression-spring).

I don't recommend ever stripping the dizzy down. There’s rebuild kits sold on eBay for Necam, and usually these are not required. Unless the lower diaphragm goes (in the bottom of the dizzy) you'll not need those kits. If swished out with injector-cleaner. you don't need to strip either. LPG runs dirty compared to CNG but repeated applications usually shift the heavy-ends. Do this every 5-6000 miles.

Fill and leave to soak in injector cleaner. Put a 2p coin over the opening to stop evaporation of the cleaner and leave it for 2-3 hours.
Injector cleaner for petrol is ideal. Wynns or Comma is fine. Specialist LPG cleaner I think is the same stuff, but twice the price. Injector cleaner for petrol works for me.

Fill to 5-10mm from top. Put a large coin, (2p piece is good) over the opening and let it soak 3-4 hours. 2p is there to stop dirt and injector-cleaner evaporating.

You are cleaning the V shaped slots you can just about make out if you look to the bottom of the cylinder/barrel of the dizzy. In bad cases, a 0.15 mm and a pair of fine long-nose pliers to push the feeler through the slots works… just.

Put a pea sized or smaller ball of grease in the keyway on the stepper motor shaft (I do NOT mean the PISTON!). When you’rve done that lubricate the piston with GT85. Do NOT use WD40, it contains silicon. You will damage your 02 sensor. Assemble: Watch for the O-ring sitting on the neck of the stepper (usually Brown in colour). There's 1 x O-ring, a spring and a spring-washer between the stepper and the dizzy. Do not F*CK this up! Wrong assembly will see you cry in your beer. You will fry your control module. So be very careful - put this lot back in the orientation and the order as you found it. Do not omit the large spring washer.

The stepper motor is at the route of most of the bad-mouthing of what is otherwise a very simple system that works well. Keep everything clean and cool, and it all works well enough. Hence…

Moving your stepper motor.
If you own a later P2 2000-2005 car, and most of you do, I would strongly advise you to move your Distributor/ Stepper Motor Assembly. if the distributor is not cleaned ‘heavy ends’ will burn- out these motors, yet there’s another reason…

Sited such that cooked by the radiator, this heat is the source of many BiFuel Volvo problems. This location also turns a 2 mins cleaning job into a major ball-ache., hence it fails to be done. Move the Distributor/ Stepper Motor Assembly out of this heat, I suggest you remount it to the battery area, in cool air.

1) You will need longer hose (if I recall 16 & 8mm).
2) Lengthen the wiring. Solder these wires, DO NOT bodge this!

Use Scotchloks or Chocolate Block terminals or other idiocies. Electronic components need soldering! Do not use heating grade orange butane/propane hose. The stuff you want is marked CNG/LPG. Find the hose you require on eBay.

Volvo should never have located these motors in such a position. Come on, opposite the battery, the main ECU and transmission ECU gets their own air-cooled box! Move your stepper, left where it is, stuck in traffic-jam for 20 mins this summer, it'll cook.

Maintenance: Your stepper.
The stepper-motor is required to whizz a piston up and down in the distributor. It responds to your right foot as you move it.

There’s two versions of the Necam Stepper:
Type A version was fitted to some CNG versions and Vauxhalls, Opels and Transits. You’ll find those for £40 odd. Sadly, they only fit the S40, S60 and pre 1998 V70s.
Type B has a flat top and is unique to Volvo. All P2 V70 and S80 cars have these. it is hard to find. It comes with the aforementioned unique price.

Both CNG and LPG cars use the same stepper motor. The does distributor differs between CNG and LPG. The difference is the size of the V slots in the cylinder. Identified by Red or Green labelling, I think Red is CNG.

Maintenance: Filters
These were often omitted from the large 16mm feed pipe into the dizzy. This made things worse. These can be found on eBay for £5-6 when Volvo want £90.00!?

Common Faults:
Most are cleaning or stepper motor related:

1) Random cutting out:
If your Bifuel randomly cuts out... if you car runs fine, cuts out and then might, or might not, start right away, you have a stepper motor problem. Tomorrow it’s fine, ad infinitum, until it cuts out again. A known issue. Where cutting out is random in car that otherwise fine (once you have it running), it’ll be a stepper motor problem. This problem will gradually get worse, unless your car refuse to run LPG/CNG at all. This distinct from lumpy running and other issues.

2) Rough running only on LPG/CNG fine on Petrol:
Indicate problems with your regulator and/or distributor. First place to look would be a dirty distributor. Don’t leave it, else more costly parts will be damaged. See above.


3) Poor starting on Petrol is often a worn regulator diaphragm. There’s is a bubble test. Details later.

That’s enough for today. I’ll do more faults later. Please put you queries to another post

WORK IN PROGRESS